1. Field of the Invention
This invention is generally directed to fluid flow control valves and, more particularly, to valves which are responsive to the temperature of fluids flowing in a passageway for automatically activating the valve to prevent or reduce fluid flow therethrough until the temperature of the fluid is below a predetermined activation temperature. The controllers of the present invention are particularly adaptable for liquid supply lines used for showers, bathtubs, sinks and the like, but also have utility in other areas wherein it is necessary to control the flow of a liquid, or other fluid, to terminate or partially terminate flow in the event the fluid temperature is above a predetermined temperature. In one embodiment, the controllers are used to maintain a generally constant temperature of a supplied fluid by functioning as a hot/cold fluid mixer.
2. History of the Related Art
There are many environments in which it is necessary to control the flow of hot gases or liquids to ensure industrial processing or to protect individuals from injury due to exposure. By way of example, in commercial and residential hot water supply systems intended for personal use, water temperatures will frequently exceed 125.degree. to 130.degree. F. At these temperatures, an individual can easily become scalded or burned by being in contact with the liquid in a matter of a few seconds. The requirement to regulate the temperature becomes even more critical in commercial environments where a large source of hot water supply is necessary during relatively short demand periods, such as in morning and evening hours. Often, temperatures are elevated in boilers or heaters of a large system so that a sufficient source of hot water is available to a great number of users at a given time. Even in household environments, a hot water supply may be set to a regulated temperature in excess of 130.degree. F. for purposes of providing sufficiently hot temperatures for dishwashing and clothes washing. Under these circumstances, it is critical to ensure that such hot water is properly mixed with sufficiently cold water before an individual bathes, showers or washes.
One of the problems inherent with regulating fluid supplies depending upon temperature is the cost of a control system which can adequately function in a particular environment. Historically, the use of electronically controlled valves has not been satisfactory for commercial and residential uses. However, through the development of temperature sensitive metal alloys, it has been possible to create valves which are mechanically actuated in response to the temperature of fluids flowing through the valves.
Such mechanically operated valves incorporate spring elements made of metal alloys which are sensitive to temperature to vary the force of the springs depending upon the ambient temperature to which they are exposed. Such springs are referred to as shaped memory alloys, which exhibit a first biasing force regulated by their stiffness in a martensitic state, but which exhibit a greater force at elevated temperatures in their austenitic state. Therefore, such alloys can be treated so as to exhibit a transformation from a martensitic to an austenitic state at predetermined temperatures so that springs constructed therefrom automatically change their biasing force dependent upon temperature. Examples of valves incorporating shaped memory alloy spring elements are disclosed in U.S. Pat. Nos. 4,778,104 to Fisher, 4,848,388 to Waldbusser, 5,259,554 to Ewing, et al. and 5,261,597 to Perlman, et al.
There remains a problem with the prior art valves which utilize shaped memory alloy springs to automatically regulate flow of a gas or liquid through a supply line. Many valves are not constructed to operate consistently within a preselected temperature range, especially if the pressure within a supply line varies. In most systems, the spring elements are placed in line with the fluid flow through a valve and, therefore, the valve elements are subject to variations in fluid pressure created in either the opening or closing of the valves. Further, many prior art valves which provide for automatic control of a valve mechanism dependent upon the temperature of the fluid flowing therethrough do not allow for a manual override or a manual resetting of the valves. There are many instances in which a manual override would be beneficial for resetting a valve.